Pulmonary embolism (PE) caused by emboli (blood clots) from deep venus thrombosis (DVT) is a major cause of death in otherwise healthy adults, many occurring without clinical warning and earning PE the reputation as "silent killer". Great need exists in clinical practice for an unattended device to detect venous embolization. The demonstrated capability of Doppler ultrasound to detect particularly microemboli will be the basis for constructing a new tool to accurately and cost effectively identify individuals at risk of PE which will: detect microemboli in the venous circulation, guide therapeutic measures, and determine their effectiveness. In Phase I a dual-gate Doppler was designed and constructed, and then was used to demonstrate a 25% prevalence rate of microemboli in a population of 20 patients with confirmed DVT. 80% of patients presenting microemboli had been on heparin therapy for a day or less. In Phase II, a novel device with enhancements for easy location of the pulmonary artery or femoral vein will be constructed and used to determine prevalence of microemboli in a series of patients presenting with high risk for DVT. Phase II results will be used to design a Phase III devise for the large anticipated commercial market. Proposed commercial applications: The project will lead to a unique commercial instrument with a large market potential to monitor for the presence of formed element emboli in the venous circulation from deep venous thrombosis, a major cause of pulmonary embolism (PE). Once detected, anticoagulant therapy can be administered by physicians to prevent or reduce the risk PE. Other markets and applications include a monitor for decompression bubble in divers, pilots and astronauts, embolism in neurosurgery, orthopedic surgery, and fractures of extremities.